OmniOS and SmartOS offer free-to-use platforms with KVM and bhyve hypervisors but have a steep learning curve. TrueNAS Scale and Unraid are viable options that combine the backup, storage, and ...

The Proxmox daemons eat a significant chunk of 4Gb, and there's also ZFS memory usage if you decide to use ZFS. I suppose it will be OK, but you might want to consider lighter alternatives like Incus.